Generally, automatic vending machines, money changers and the like using coins are required to distinguish denomination and authenticity of inserted coins.
Conventionally, such a type of coin distinguishing device is configured to have a single or plural magnetic coil sensors disposed at a passage through which a coin inserted through a coin insertion slot passes, to distinguish the material, thickness, size and the like of the coin, and to distinguish the denomination and authenticity of the coin based on the distinguished results.
Besides, it is also proposed to configure so to detect the thickness, size and the like of the coin by an optical sensor such as an image pickup device.
In recent years, however, altered coins, which are foreign currency having a material and a shape similar to those of domestic specie and modified so to have a pattern similar to that of the domestic specie obtained by an optical sensor or a magnetic sensor, are spreading. And, as the altered coins have become having a higher machining accuracy, a problem of difficulty in distinguishing authenticity by a conventional magnetic sensor or optical sensor is occurring. Especially, misuse of foreign currency has become a serious problem because 500-yen coins are coins of large denominations.
Therefore, to distinguish such altered coins, it is necessary to distinguish such coins with a higher accurately, and there have been proposed various methods of using a pattern formed on the surface or side of the coin.
For example, Japanese Patent Application Laid-Open No. 9-167270 discloses a method by which the side of a coin is irradiated with light, reflection light is detected by an optical sensor to obtain an image of the side of the coin, and the presence or not of a cyclic linear uneven pattern (hereinafter called as the mill) formed on the side of the coin is detected based on the obtained image of the side of the coin.
Japanese Patent Application Laid-Open No. 10-83471 discloses a method by which the outer periphery portion of the surface of a coin is irradiated with light, reflection light is detected by an optical sensor to obtain an image of the outer periphery portion of the coin, a projecting pattern (pearl) imprinted concentrically at equal intervals on the outer periphery portion of the coin is detected based on the obtained image of the outer periphery portion of the coin.
Besides, there have been proposed configurations combining various types of methods to distinguish coins with a higher accurately, and Japanese Patent Application Laid-Open No. 10-222716 discloses a method by which both surfaces and side of a coin are irradiated with light, beams of reflection light are collected by mirrors and detected by an optical sensor to obtain the images of the both surfaces and side of the coin at the same time, and the coin is distinguished based on the obtained images of the both surfaces and side of the coin.
But, the prior art disclosed in Japanese Patent Application Laid-Open No. 9-167270 and Japanese Patent Application Laid-Open No. 10-83471 have limitations in improving a distinguishing rate (a rate of distinguishing coins accurately) when a coin is distinguished based on only the images of the surfaces or side of the coin, and the prior art disclosed in Japanese Patent Application Laid-Open No. 10-222716 has disadvantages that two lighting means, two mirrors for collecting beams of reflection light from the both surfaces of the coin to an optical sensor and two deflection plates for preventing the beams of light from the two lighting means from mutually influencing are required to obtain the images of both surfaces of the coin, resulting in a complex structure and having a difficulty in downsizing the device.